基于CEL有限元法的大管径钢管桩贯入海基过程的承载力分析

鉴于耦合欧拉-拉格朗日(Coupled Eulerian-Lagrangian, CEL)有限元方法在计算分析接触大变形问题时的优势，建立了大管径钢管桩贯入海基的CEL有限元模型，即在被贯入的海基层采用欧拉有限元法建模，其它层采用拉格朗日有限元法建模，两者之间通过罚函数的接触算法进行耦合．在欧拉有限元模型中，采用算子分裂技术．为兼顾计算模型的精度和效率，本文先对模型的网格密度和贯入速度进行稳定性分析，以此确定合适的网格模型和适宜的贯入速度，同时验证CEL方法在贯入模拟中的可行性．随后针对不同土体类型和不同土体参数变化，探究土体贯入阻力随贯入深度的变化规律．计算结果表明砂土的贯入阻力最大，粉砂土次之，粘土的贯入阻力最小；且贯入阻力对土体内摩擦角的变化最为敏感，对土体粘聚力的变化比较敏感，而对土体模量的变化不敏感．     

土中爆炸冲击混凝土道面的数值模拟

炸药在多相介质中的爆炸是气态爆轰产物和固态介质之间的耦合作用问题，对其进行数值模拟一般不考虑炸药而直接将爆轰压力加在介质上，而耦合方法对炸药和其周围的介质进行离散，炸药和介质采用统一的控制方程，通过界面条件实现相互作用。任意拉格朗日欧拉（Arbitary Lagrangian and Eularian）法，是最近兴起的适用于计算固体大变形问题的数值计算方法。将其引入爆炸力学计算，可以避免由于物质的大变形引起的单元畸变和计算困难。同时混凝土的损伤模型，更加符合混凝土在高应变率加载条件下的力学特性和破坏机理。将这三种方法引入数值模拟，计算结果与相关试验结果有较好的吻合。     

岩土工程下沉贯入数值模拟方法研究进展

岩土工程下沉贯入领域的数值分析,由于结构物贯入时网格变形过大而产生扭曲畸变等问题,常会造成收敛困难甚至计算结果失真.采用合适的数值方法分析此类问题颇具挑战性.本文系统介绍了近年来对于岩土下沉贯入数值模拟的研究现状和发展动态,对各种数值模拟方法的相关原理、主要特征以及优缺点进行简要的探讨.并简要介绍耦合的欧拉-拉格朗日(coupled Eulerian--Lagrangian,CEL)有限元法的基本原理,通过不排水条件下的条形基础贯入问题和砂土中桩的静压下沉示例分析,表明CEL有限元法在模拟岩土贯入问题时计算结果的准确性和较其他模拟方法的优势.文中所阐述的岩土贯入分析数值模拟方法可供从事岩土贯入分析的相关学者借鉴参考.     

有限变形时材料性质张量的选取

在有限变形时导出了用欧拉观点描述的与用拉格朗日观点描述的材料性质张量之间用矩阵形式表达的转换关系，指出正确应用这个关系时将到唯一的计算结果，与计算方法无关，建立在连续体力学中应将材料性质实验结果与欧拉观点描述的材料性质张量相对应。     

基于ALE算法的V形楔形体入水的水动力特性分析

结构入水问题是一种复杂的流固耦合过程,涉及到固体力学、流体力学、冲击动力学和计算力学等相关力学分支的交叉与融合.论文基于非线性显式动力分析方法,采用任意拉格朗日-欧拉算法(水域采用欧拉描述,固体结构采用拉格朗日描述),并用罚函数方法控制结构与流体之间的耦合作用,对二维V形楔形体垂直入水的初期过程进行了数值仿真.通过数值仿真,分析了楔形体底部压力分布情况,讨论了网格密度、接触刚度以及阻尼系数对数值计算结果的影响,并将数值结果与Wagner理论解进行了对比分析,验证了ALE方法的可靠性.     

非线性流体弹性力学研究进展

流体弹性力学理论是用来描述液体、气体的运动与弹性结构相互作用的学科. 由于其交叉性质, 涉及到人类日常生活中的方方面面, 致使在许多学科和工程领域中都成了主要的研究内容, 并得到了广泛地应用. 本文在阐述研究流体与弹性体相互作用的非线性问题的重要意义及分类方法的基础上, 介绍了非线性流体弹性力学的特征、研究现状和非线性问题的研究方法, 如理论分析法、实验分析法、数值分析法和半解析法等的进展; 介绍了描述介质相互作用的任意拉格朗日-欧拉(ALE)法、相容拉格朗日-欧拉(ULE)法、 单一拉格朗日(SL)法和单一欧拉(SE)法之间的关系, 并且对这些研究方法的优缺点进行了比较; 介绍了非线性流体弹性力学研究的内容和在气动弹性力学、水弹性力学、环境流体弹性力学、 微尺度流体弹性力学和涡激振动等领域中的应用; 阐述了非线性流体弹性力学的发展前景和所面临的任务.     

一种结合Roe格式的高精度半拉氏方法

针对守恒形式的欧拉方程组, 构造了一种结合Roe格式的守恒型有限体 积形式的半拉氏方法. 通过发展一种基于Roe特征速度的拉氏质点回溯方法, 由此来计算 半点的流量并作为边界通量的近似, 使得这种半拉氏方法在时空离散上达到二阶精度, 并 且保证了守恒性. 其中回溯点处物理量采用本质无振荡格式(ENO)方法进行插值重 构得到, 不需要增加人工黏性且避免了有限体积多矩半拉氏方法中限制器选择的问题, 又能够达到时空的高阶精度. 方法简便, 易于实现, 兼具拉氏方法和欧拉方法的优点. 一维和二维数值算例表明, 此方法对激波和接触间断都取得了满意的模拟效果, 可用于可压缩复杂流动问题的计算.     

二维磁流体力学ALE数值模拟

介绍采用ALE方法进行的电磁内爆二维磁流体（MHD）力学模拟。二维MHD力学模拟的ALE方法分成拉格朗日、网格重分、对流输运三步。拉格朗日步采用文献[4]的时间分裂法，分成辐射冷却、热扩散、磁扩散、Lagrangian流动四步求解，并对Lagrangian流动步的方法进行了改进，消除了其拉氏计算的质量损失等。编制了二维计算程序并通过验证，获得的二维电磁内爆不稳定性发展与文献[2，5，11]吻合。     

一种基于几何重构的Youngs-VOF耦合水平集追踪方法

针对界面追踪方法中拉格朗日方法和欧拉--拉格朗日方法计算效率低、不适用大变形、不能应用于三维数值计算模型等问题,研究了一种效率高、界面清晰、适用于三维模型的计算气液两相界面迁移特性的欧拉运动界面追踪方法,该方法将"米"状相邻单元Youngs方法用于运动界面重构,将Youngs-VOF和水平集通过几何方法耦合,提高运动界面精度,克服了VOF和水平集方法存在的缺陷,避免了利用高阶导数本身的稳定性去求解水平集对流方程和距离函数方程."米"状相邻单元Youngs方法避免了数值耗散、数值色散性以及非线性效应引起的捕捉界面模糊的情况.Youngs-VOF耦合水平集方法既保证了计算界面时的稳定性,与拉格朗日方法相比又提高了计算效率.利用Youngs-VOF耦合水平集方法与VOF方法对单个气泡在水中上升过程数值计算与实验对比并对经典剪切流场中圆形运动界面模型的数值计算,验证了Youngs-VOF耦合水平集方法的有效性并比VOF方法捕捉界面更清晰、锐利;通过对溃坝--自由表面流动过程数值计算并与实验进行对比,验证了Youngs-VOF耦合水平集方法的稳定性以及对三维数值模型的适用性.      

两种颗粒湍流扩散模型数值模拟气液两相流泄漏扩散的比较

采用相间耦合的欧拉-拉格朗日方法，模拟了装有液化气（丙烷）的容器出现小孔或裂缝时，发生泄漏后的气液两相扩散过程。分别应用随机轨道模型及颗粒群模型来考察湍流对液滴扩散的影响，并与确定性轨道进行了比较。给出了数学物理模型，计算结果与实验数据进行了对比。结果表明:采用随机轨道模型能较好地描述液滴的湍流扩散，适用于有液相蒸发的两相流扩散问题。     

Modeling finite thickness slab perforation using a coupled Eulerian–Lagrangian approach

A coupled Eulerian–Lagrangian (CEL) method can be used to model many types of dynamic events. Projectile penetration through solids is particularly well-suited to a CEL method. In this study the CEL method in the commercially-available code Abaqus was used to model a near rigid projectile perforating finite thickness concrete slabs. A near rigid projectile can be modeled as a Lagrangian material with distinct material interfaces, while the solid target can be modeled as an Eulerian material capable of large deformations. An improved concrete constitutive model is also described that was implemented into Abaqus as a user material model. A simplified stochastic model was also implemented to capture some of the heterogeneous nature of concrete. The CEL simulations are compared to experimental data to demonstrate the utility of this method for this type of perforation event.     

粘性流体中弹性板振动的有限元耦合问题

流体－结构耦合作用问题是工程中比较常见的问题，具有重要意义，由于流体计算的复杂性，迄今为止，大部分的流体－结构耦合分析都是建立在对流体充分简化的基础上，尤其是将流体视为无粘、无旋的理想流体。该文在近年来前人工作的基础上，发展了一种流体－弹性结构耦合计算模式。流体视为不可压、有粘的介质，流场没有自由表面。该文采用ＳＵ／ＰＧ方法形成流体的有限元方程，采用ＡＬＥ格式处理流体和结构之间的移动界面。采用预估     

An embedded approach for immiscible multi‐fluid problems

An embedded formulation for the simulation of immiscible multi‐fluid problems is proposed. The method is particularly designed for handling gas–liquid systems. Gas and liquid are modeled using the Eulerian and the Lagrangian formulation, respectively. The Lagrangian domain (liquid) moves on top of the fixed Eulerian mesh. The location of the material interface is exactly defined by the position of the boundary mesh of the Lagrangian domain. The individual fluid problems are solved in a partitioned fashion and are coupled using a Dirichlet–Neumann algorithm. Representation of the pressure discontinuity across the interface does not require any additional techniques being an intrinsic feature of the method. The proposed formulation is validated, and its potential applications are shown. Copyright © 2015 John Wiley & Sons, Ltd.     

GEL方法在一维双界面问题中的应用

用ghost-fluid Euler-Lagrange(GEL)耦合数值方法,对二维GEL计算程序(其中Euler流场计算采用以SCB格式编制的二阶计算程序,Lagrange域计算采用DEFEL二维动力有限元程序)进行扩展,将程序应用于多界面问题.算例为空气和水的一维双界面黎曼问题,获得了密度、速度和压力结果,并通过i...     

A time splitting fictitious domain algorithm for fluid–structure interaction problems (A fictitious domain algorithm for FSI)

A Finite Element Method in mixed Eulerian and Lagrangian formulation is developed to allow direct numerical simulations of dynamical interaction between an incompressible fluid and a hyper-elastic incompressible solid. A Fictitious Domain Method is applied so that the fluid is extended inside the deformable solid volume and the velocity field in the entire computational domain is resolved in an Eulerian framework. Solid motion, which is tracked in a Lagrangian framework, is imposed through the body force acting on the fluid within the solid boundaries. Solid stress smoothing on the Lagrangian mesh is performed with the Zienkiewicz–Zhu patch recovery method. High-order Gaussian integration quadratures over cut elements are used in order to avoid sub-meshing within elements in the Eulerian mesh that are intersected by the Lagrangian grid. The algorithm is implemented and verified in two spatial dimensions by comparing with the well validated simulations of solid deformation in a lid driven cavity and periodic elastic wall deformation driven by a time-dependent flow. It shows good agreement with the numerical results reported in the literature. In 3-D the method is validated against previously reported numerical simulations of 3-D rhythmically contracting alveolated ducts.     

聚能射流三维数值模拟

研究三维多介质界面处理及数值模拟问题。采用拉格朗日法、欧拉法相结合的方法在矩形网格上离散差分基本方程组；在欧拉步中引入模糊方法处理界面，计算各输运量；编写了数值模拟程序，并对线型装药金属罩聚能射流模型进行模拟。证明模糊界面描述和模糊输运计算有效、可行。     

A 3D finite element ALE method using an approximate Riemann solution

Arbitrary Lagrangian–Eulerian finite volume methods that solve a multidimensional Riemann‐like problem at the cell center in a staggered grid hydrodynamic (SGH) arrangement have been proposed. This research proposes a new 3D finite element arbitrary Lagrangian–Eulerian SGH method that incorporates a multidimensional Riemann‐like problem. Two different Riemann jump relations are investigated. A new limiting method that greatly improves the accuracy of the SGH method on isentropic flows is investigated. A remap method that improves upon a well‐known mesh relaxation and remapping technique in order to ensure total energy conservation during the remap is also presented. Numerical details and test problem results are presented. Copyright © 2016 John Wiley & Sons, Ltd.     

极端变形问题的物质点法研究进展

物质点法采用了拉格朗日和欧拉双重描述,将物体离散为一组在固定于空间的网格(欧拉描述)中运动的质点(拉格朗日描述),有效地综合了拉格朗日法和欧拉法的优点,是分析冲击爆炸等极端变形问题的一种有效方法. 本文系统总结了本课题组近年来针对冲击、爆炸和流固耦合等极端变形问题在物质点法算法方面的研究进展,并简要介绍了开发的三维显式并行物质点法数值仿真软件MPM3D及其在超高速碰撞、侵彻、爆炸、边坡失效、金属切削和流固耦合等问题中的应用.     

A virtual experiment for partial space elevator using a novel high-fidelity FE model

Nonlinear Dynamics - This paper developed a high-fidelity virtual experiment for a partial space elevator using nodal position finite element method with arbitrary Lagrangian–Eulerian...     

Multiscale simulations and experiments on water jet atomization

Numerical simulation of primary atomization at high Reynolds number is still a challenging problem. In this work a multiscale approach for the numerical simulation of liquid jet primary atomization is applied, using an Eulerian-Lagrangian coupling. In this approach, an Eulerian volume of fluid (VOF) method, where the Reynolds stresses are closed by a Reynolds stress model is applied to model the global spreading of the liquid jet. The formation of the micro-scale droplets, which are usually smaller than the grid spacing in the computational domain, is modelled by an energy-based sub-grid model. Where the disruptive forces (turbulence and surface pressure) of turbulent eddies near the surface of the jet overcome the capillary forces, droplets are released with the local properties of the corresponding eddies. The dynamics of the generated droplets are modelled using Lagrangian particle tracking (LPT). A numerical coupling between the Eulerian and Lagrangian frames is then established via source terms in conservation equations. As a follow-up study to our investigation in Saeedipour et al. (2016a), the present paper aims at modelling drop formation from liquid jets at high Reynolds numbers in the atomization regime and validating the simulation results against in-house experiments. For this purpose, phase-Doppler anemometry (PDA) was used to measure the droplet size and velocity distributions in sprays produced by water jet breakup at different Reynolds numbers in the atomization regime. The spray properties, such as droplet size spectra, local and global Sauter-mean drop sizes and velocity distributions obtained from the simulations are compared with experiment at various locations with very good agreement.